The font-weight property allows you to choose how thick or
thin the characters of a text appear. This is referred to as boldness.
Boldness is a relative, not fixed, quantity which is determined by your
individual computer and/or browser.

Many browsers only recognize normal and bold font weight.

normal

The normal value is the default. On the numeric scale running
from 100 to 900, normal is usually considered to be 400.
By declaring normal, you can ensure that any previous declaration
will not effect a selected text.

bold

The bold value corresponds to the <B> tag in HTML. On
the numeric scale running from 100 to 900, bold
is usually considered to be 700.

bolder

The bolder value makes the character appear thicker in size
and, hence, increases the boldness. The amount of change will be determined
by the individual computer/browser.

lighter

The lighter value makes the character appear thinner in size
and, hence, decreases the boldness. The amount of change will be determined
by the individual computer/browser.

100 ... 900

The 100,200,300,400,500,600,700,800,900 values provide nine
steps in range of boldness. The larger the number, the greater the boldness.
This is a relative numeric scale where 400 usually equates to
normal and 700 to bold. The amount of change caused
by each step will be determined by the individual computer/browser.